Radiographic imaging of body parts is well known and extremely useful as a diagnostic tool in the medical arts. Radiographic imaging involves positioning a part of a patient to be imaged denoted as the "structure of interest" under an X-ray tube, exposing the structure of interest to an X-ray beam, and recording the X-ray image on an image receptor. The receptor in most instances is a radiographic film disposed in contact with an intensifying screen. The film and screen are kept in tight contact during the exposure in a film holder or cassette. After exposing the structure of interest, the film is removed from the cassette, may be labeled with the patient's name and other identifying information, and then developed.
The diagnostic value of radiographic imaging as described above is dependent on the quality of the radiographic image, which in turn depends on an interplay of several factors. One of the more important of these factors is the process by which the radiographic image is developed. Radiographic images which are made on radiographic films are generally developed in devices called "film processors." Film processors are subject to many variations which are functions of the kind of film processor used to develop the film, the age and quality of the chemicals in the film processor which develop the film, the duration of time the film is processed, and the temperature and pH of the chemicals. Since the diagnostic value of a radiographic image is highly dependent upon the quality of the radiographic image, it is imperative that the film processor be well controlled in order to optimally develop the image. It is also important to minimize fluctuation of processor parameters from film to film.
As is known by those with skill in the art, an X-ray image of acceptable diagnostic quality generally comprises an image of the structure of interest as a series of gray levels. Examination of the gray level image indicates whether the structure of interest is healthy, or whether the structure of interest may contain certain diseases such as, for example, cancer.
Since the quality of the radiographic image is highly dependent on the film processor, the film processor must be periodically tested to ensure that the images which are produced have a high diagnostic quality. There are several prior methods currently in use to test film processors. One such method involves the use of a "sensitometer" and a "densitometer." A sensitometer is an instrument which impresses a series of graduated exposures on a photographic material. In these sensitometers, a light source of known luminous intensity is displaced at a fixed distance from an exposure plane and emits radiation of known spectral intensity. The surface of the photographic material is positioned to substantially coincide with the exposure plane.
In the sensitometer, an exposure modulating device is located between a film and the light source. If the exposure modulating device is removed, the entire photosensitive material may be uniformly illuminated. However, the purpose of the exposure modulating device is to alter this condition so that various areas of the photosensitive surface are subjected to a series of different exposures, thereby forming a graded density pattern on the photosensitive surface which is developed as a series of gray levels. This density pattern is a function of the type of film and the action of the processor.
After the film is developed by a film processor with the sensitometric graded density gray scale level pattern imposed thereon, a densitometer is used to measure densities created by the exposure modulated device. In this fashion, the graded density pattern, which may be precalibrated in terms of various parameters such as for example, film speed, base and fog, and contrast, can be used to gauge and evaluate the performance of the film processor.
Various other methods and apparatus have been used to test film processors. Examples of these other methods and apparatus are sensitometric film strips which have been pre-exposed and aged, and are then packaged to be sold commercially. These pre-exposed strips are used in conjunction with a readout device. To check the film processor, one of the strips is developed and inserted into the readout device. When the film is withdrawn, the readout device produces a light signal which indicates the temperature and the condition of the chemicals in the processor. No digital readout is provided and no quantitative indications of the condition of the film processor can be determined.
Methods to check film processors by measuring the pH of the chemicals and the operating temperature of the film processor are also known in the art. It has also been known to use "step wedges" to create a graded pattern on radiographic films. These step wedges are generally constructed of an X-ray absorbing material and are used to determine the effect that the X-rays have on the image quality, but not the effect that the film processor has on the image quality.
The aforementioned prior methods for testing a film processor which develops radiographic images do not satisfy long-felt needs in the art for methods and apparatus to test film processors that are quick, efficient and standardized to particular exposures and film types. The recommended frequency for conducting sensitometric and densitometric tests is daily. However, in the realities of the clinical environment, daily testing of film processors is often not completed.
There are many reasons that daily testing is not always accomplished. Chief among these reasons are that special training and equipment are needed, and additional X-ray film is required. As a result, the diagnostic quality of X-ray images is often severely compromised. Poor film processor performance results in degraded radiographic image quality and could ultimately result in failure to detect diseases. This is particularly devastating, for example, in radiographic images of female breasts called "mammograms" where diagnostic features are often subtle, and early detection of breast cancer is often critical to future survival.
The inventor of the subject matter herein claimed and disclosed has recognized a long-felt need in the art to eliminate the need for repeat densitometric readings of test films to monitor the performance of film processors. There are further long-felt needs in the art to minimize the use of extra test films to monitor processor performance, and also to provide the ability to record the effect of processing on the radiographic image for recall during subsequent examinations. A permanent record of processor monitoring for quality assurance and medico-legal needs is also desired in the art.